Purpose. In difficult visual searches for a specified target, attention and eye movements are directed towards stimuli with features belonging to that target. Can search be directed simultaneously by more than one target? In most cases, searching for two targets simultaneously results in lower performance compared with conducting two independent searches, one for each target. By tracking eye movements during search, we were able to explore why there is a cost in searching for two targets simultaneously.

Method. In this search task, the stimuli were color-shape conjunctions, each comprising a combination of simple rectangular components, combined in one of four different ways. Each object was made of one or two colors, with a range of different colors being used across different objects. Each target was defined by a combination of shape and color. In Experiment 1, the targets differed from each other in shape, whereas in Experiment 2 the targets differed in both color and shape. Participants were students, with no previous experience in this search task.

Results. During single and dual-target searches for a target or targets of one color, with distractors of many different colors, most fixations were targeted at objects with a color similar to the target. However, in simultaneous search for two different-colored targets, there were more fixations to objects with colors that were different from either target.

Conclusion. Selection by color is very effective in single-target search and in dual-target search for same-color targets, but when two targets vary in the color dimension as well as shape, color selection breaks down to some extent, allowing the selection of objects that have a color that is not similar to either target.